GB2454183A

GB2454183A - Joist cap extension

Info

Publication number: GB2454183A
Application number: GB0721218A
Authority: GB
Inventors: Robert Sinclair Hanks; Kenneth Stanley Targett
Original assignee: CAPIT BUILDING PRODUCTS Ltd
Current assignee: CAPIT BUILDING PRODUCTS Ltd
Priority date: 2007-10-30
Filing date: 2007-10-30
Publication date: 2009-05-06
Anticipated expiration: 2027-10-30
Also published as: GB0721218D0; GB2454183B

Abstract

An extension piece 26 is disclosed for a joist cap 10 of the type having an end wall to cover the end face of a joist that is to be built into a wall, a top wall and a pair of side walls 18 extending from the end wall to cover the top and sides of an end portion of the joist, and flange portions 24 projecting outwardly from the side walls for being embedded in mortar of the wall, or for covering the face of the wall to either side of the joist, as the wall is built up around the end portion of the joist. The extension piece comprises: a main channel portion 28 for receiving the joist cap and having an end wall and a pair of side walls 32 for overlapping the end wall and side walls, respectively, of the joist cap; and a pair of mutually-facing flange-receiving channel portions 34 projecting outwardly from the side walls of the extension piece for receiving the flange portions of the joist cap. The extension piece and the joist cap can be moved telescopically to vary the effective length B of the extension piece and joist cap. The extension piece can therefore be used with such a joist cap to increase the size and range of joist depths with which the joist cap can be satisfactorily used.

Description

TITLE

Joist caps

DESCRIPTION

This invention relates to joist caps.

As is discussed in the introduction of patent document GB2426987B, timber joists were traditionally supported by having their ends embedded in holes in the supporting walls.

However, if the timber used for the joist is not thoroughly seasoned, the end of the joist can, in time, shrink and split, leaving gaps through the wall, causing draughts and reducing the thermal-insulation, acoustic-insulation and fire-retardant properties of the wall. More recently, joist hangers have been used. With a joist hanger, the end of the joist is not directly supported by the wall, but instead stops short of the wall and sits in a cradle portion of the joist hanger, and a hook portion of the joist hanger is embedded in the wall. Joist hangers solve the air leakage problem to some extent, but they introduce their own problems, which can result in a weak structure, or in collapse of the building while it is under construction. To solve these problems, a return to the embedded-end method of joist support has been proposed, but additionally using a joist cap that provides a seal in the case where the joist shrinks or splits.

A number of joist caps have been proposed, as described in patent documents GB2394234B, GB2420799B, GB2420800B and GB2426987B of Vaughan and Hennen, GB2392928B and GB2393459B of Simpson Strong-tie, GB2405881A of Manthorpe and EP1633938B1 of Easy Joist. A joist cap of the type proposed in GB2426987B and as covered by British Board of Agrement certificate No. 07/4459 is shown in Figures 1A to 2 of the accompanying drawings.

Each of these known joist caps 10 has an end wall 12 that covers the end face of the joist 14, and a top wall 16 and a pair of side walls 18 extending from the end wall 12 to cover the top and sides of an end portion of the joist 14. The side and top walls 16,18 of the joist cap are embedded in the wall 20 (which is shown partly built in Figure 2), and even if the joist 14 shrinks or splits, the end wall 12 of the joist cap 10 serves to maintain a seal to prevent air leakage through the wall. Some of the joist caps described in the documents mentioned above also have a bottom wall that covers the bottom of the end portion of the joist, and the joist sits on the bottom wall. However, some of the joist caps described in the Vaughan and Hennen patents are devoid of a bottom wall, as shown in Figures 1A to 2. The lack of a bottom wall provides a number of advantages: the end of the joist 14 bears directly on the blockwork of the wall 20 so that the joist cap 10 does not interfere with the support that the wall 20 provides for the joist 14; * any moisture in the end of the joist 14 can be absorbed and dispersed by the blockwork of the wall 20, rather than being trapped; * once the joist 14 has been laid, it is not necessary to lift the end of the joist 14 in order to fit the joist cap 10; * in the case where the joist cap 10 is injection-moulded from plastics material using a simple mould with mould faces that are all generally parallel or at right-angles to each other, the side walls 18 of the joist cap 10, when released from the mould, naturally converge in the direction away from the rear wall 12, with an angle of convergence that progressively increases from the top to the bottom of the joist cap 10, so that the joist cap 10 naturally grips the end portion of the joist 14 and stays in place while the wall 20 is being built around the joist 14 and joist cap 10; * in the case where the joist cap 10 is substantially taller than the depth of the joist 14 to which it is to be applied, the bottoms of the end and side walls 12,18 can be cut away so that the joist cap 10 is a better fit for the joist 14 but without interfering with the functionality of the joist cap 10; and * the side walls 18 of the joist caps 10 can be interdigitated so as to reduce the space required for storage and transportation.

In addition to the lack of a bottom wall, some of the joist caps of the Vaughan and Hennen patents have outwardly projecting flange portions 22,24 at the front edges of the top and side walls 16,18. The flange portions 22,24 are embedded in the mortar of the wall 20 within the thickness of the wall 20 as the wall 20 is built up around the joist cap 10 and the end portion of the joist 14. The embedded flange portions 22, 24 serve: * to improve the seal between the joist cap 10 and the wall 20; * in combination with the open-bottomed feature, to enable a particular size of the joist cap 10 to be used with any thickness of wall 20 (greater than a predetermined minimum) while: o maintaining the effectiveness of the seal; and o enabling the joist 14 to be supported by substantially the full thickness of the wall 20.

By contrast, the joist caps that have been put on the market and are covered by the Simpson Strong-tie patents and the Manthorpe application (BBA certificates Nos. 04/4170 and 04/4118) have a much larger flange that is exposed and bears against the inner face of the wall.

This limits the length of the end portion of the joist that overlaps, and is therefore supported (indirectly through the bottom wall of the joist cap), by the wall. Furthermore, the joist cap that has been put on the market and is covered by the Manthorpe application also has exposed tabs projecting from the rear wall of the joist cap that bear against the rear face of the building wall.

This limits the thickness of the building wall with which one size of joist cap can be used to one particular building wall thickness. Moreover, the joist cap that has been put on the market and is covered by the Easy Joist patent (BBA certificate No. 06/4293) is devoid of any such flanges or tabs. It can therefore be used with any thickness of wall greater than or equal to the depth of the joist cap. However, when used with a building wall of greater thickness than the depth of the joist cap, because of the presence of the bottom wall of the joist cap, the end portion of the joist is supported, through the bottom wall of the joist cap, only over the joist cap depth, not over substantially the whole thickness of the building wall. It might be possible to fill the gap, where the end portion of the joist overiaps the building wall but is not supported by the bottom wall of the joist cap, with mortar. However, doing this after the joist and cap have been laid on the wall would present difficulties in obtaining a satisfactory fill of the gap. Doing this immediately before the joist and cap are laid entails an additional mortaring process.

In view of the above, in order to obtain full support of the end portion of the joist over substantially the whole thickness of the building wall without additional mortaring beneath the end of the joist, the commercially available versions of the Simpson Strong-tie, Manthorpe and Easy-Joist joist caps all require a different size of joist cap for each wall thickness. Standard thicknesses of thermal blocks typically used in domestic house-building include 100 mm, 115 mm, 125 mm, 130 mm and 140 mm. Furthermore, in order to achieve a reasonably snug fit widthwise of the joist in the joist cap, a different size of joist cap is required for each joist width. Standard widths of traditional sawn timber joists used in domestic house-building include 38 mm, 47 mm, 63 mm, 75 mm, and 100 mm. Moreover, in order to achieve a reasonably snug fit height-wise of the joist in the joist cap, a different size of joist cap is required for each joist height. Standard heights of traditional sawn timber joists used for intermediate floors in domestic house-building include 175 mm, 200 mm and 225 mm. Accordingly, in order to obtain full support of the end portion of the joist over substantially the whole thickness of the building wall without additional mortaring beneath the end of the joist, and in order to deal with five different wall thicknesses, and provide a reasonably snug fit for five different joist widths and three different joist heights, it is necessary with the commercially-available Simpson Strong-tie, Manthorpe and Easy-Joist designs of joist cap to provide seventy-five different sizes of joist cap (5 wall thicknesses x 5 joist widths x 3 joist heights). The need for such a large product ranges has significant disadvantages for example in terms of tool-making costs, scheduling of manufacture, transportation, storage, stocking, product ordering, and use of left-overs.

By comparison, using the Vaughan and Hennen joist cap of the type shown in Figures 1A to 2, it is necessary to provide only fifteen different sizes of joist cap (5 joist widths x 3 joist heights) in order to provide a snug fit, as manufactured, for such a range of wall thicknesses, joist widths and joist heights. Furthermore, because these joist caps have an open bottom, it is possible to trim the height of the joist cap by cutting away a bottom portion of the joist cap without affecting the way in which the joist cap works. Therefore, in order to cover the variations in wall thickness, joist width and joist height discussed above, it is possible to make do with only five sizes of joist cap as manufactured (5 joist widths), leaving it to the builder to cut down the height of the joist cap, if necessary to fit a particular joist. However, this involves an additional step during fitting of the joist caps which it would be desirable to avoid.

Engineered I-beam joists are becoming more popular. An I-beam joist has upper and lower flanges joined by a thin vertical web. In order to provide high flexural rigidity to such joists their height:width ratio tends to be greater than for traditional sawn timber joists.

Furthermore, in order to provide a range of stiffnesses and strengths of I-beam joists, there has been a tendency to provide a greater range of heights than widths. For example, Finnjoist� FJI joists are offered by Finnjoist in four widths (38, 45, 58 and 89 mm) and six heights (200, 220, 240, 300, 350 and 400 mm). This exacerbates the problem of providing a complementary range of joist caps, particularly if of the type available from Simpson Strong-tie, Manthorpe and Easy-Joist, where, to deal with five different wall thicknesses, it is necessary to provide a range of one hundred and twenty different sizes of joist cap (5 wall thicknesses x 4 joist widths x 6 joist heights).

An aim of the present invention, or at least of specific embodiments of it, is to deal with the problem discussed above.

In accordance with a first aspect of the present invention, there is provided an extension piece for a joist cap of the type having an end wall to cover the end face of a joist that is to be built into a wall, a top wall and a pair of side walls extending from the end wall to cover the top and sides of an end portion of the joist, and flange portions projecting outwardly from the side walls for being embedded in mortar of the wall, or for covering the face of the wall to either side of the joist, as the wall is built up around the end portion of the joist. The extension piece of the first aspect of the invention comprises: a main channel portion for receiving the joist cap and having an end wall and a pair of side walls for overlapping the end wall and side walls, respectively, of the joist cap; and a pair of mutually-facing flange-receiving channel portions projecting outwardly from the side walls of the extension piece for receiving the flange portions of the joist cap; whereby the extension piece and the joist cap can be moved telescopically to vary the effective length of the extension piece and joist cap. The extension piece can therefore be used with such a joist cap to increase the size and range of joist depths with which the joist cap can be satisfactorily used. In one embodiment in which the height of the extension piece is about the same as the height of the joist cap, the joist cap and extension piece can be satisfactorily used with any depth of joist in the range from slightly greater than the joist cap height to slightly less than twice the joist cap height.

The end wall of the extension piece is preferably formed, at its bottom end, with an inwardly-projecting lip to enable a more effective seal to be achieved between the end wall of the extension piece and the blockwork of the wall. The bottoms of the side walls of the extension piece are preferably also formed with inwardly-projecting lips. These lips may be arranged to keep the side walls of the extension piece parallel to the sides of the joist.

The flange-receiving channel portions preferably stop short of the bottom end of the extension piece. A gap is therefore formed between the lower ends of the flange-receiving channel portions and the blockwork of the wall, permitting the use of restraint straps between the wall and the joist without interfering with the joist cap and extension piece.

Preferably, the main channel portion is open-ended at both ends thereof. In use, the joist cap therefore enters the extension piece through its open top, and the open bottom of the extension piece provides many similar advantages to those discussed above in relation to the open bottom of the joist cap, namely: * the end of the joist can bear directly on the blockwork of the wall; * any moiswre in the end of the joist can be absorbed and dispersed by the blockwork of the wall, rather than being trapped; * once the joist has been laid, it is not necessary to lift the end of the joist in order to fit the joist cap and extension piece; * in the case where the extension piece is injection-moulded from plastics material using a simple mould with mould faces that are all generally parallel or at right-angles to each other, the side walls of the extension piece naturally converge in the direction away from the rear wall, so that the extension piece naturally grips the end portion of the joist and stays in place while the wall is being built around the joist, joist cap and extension piece; and * the side walls of the assembled joist caps and extension pieces can be interdigitated so as to reduce the space required for storage and transportation.

The extension piece could be formed from plastics material by extrusion. However, it would be impossible or very difficult to form the inwardly-projecting lips during the extrusion process, and the lips would need to be formed or added after the extrusion process.

The extension piece is preferably formed by injection moulding. The inwardly-projecting lips can easily be formed using a simple two-part mould. However, the formation of the mutually-facing flange-receiving channel portions does present some difficulty when injection moulding. They could be formed by using movable cores in the mould. However, this adds to the tool-making costs and increases the production time and complexity. In order to deal with this problem, each flange-receiving channel preferably has a pair of side walls and a base, with each side wall having a series of cutaways offset from the cutaways in the other side wall of that flange-receiving channel. As will be appreciated from the following detailed description of the drawings, this enables a simple two-part mould to be employed.

Preferably, in the relaxed state of the extension piece, the side walls of the main channel portion converge towards each other in the direction away from the end wall. This produces the benefits described above through the use of a simple mould in which all of the main moulding faces are generally parallel or at right-angles to each other.

In accordance with a second aspect of the present invention, there is provided a joist cap assembly, comprising: an extension piece according to the first aspect of the invention; and a joist cap having an end wall to cover the end face of a joist that is to be built into a wall, a top wall and a pair of side walls extending from the end wall to cover the top and sides of an end portion of the joist, and flange portions projecting outwardly from the side walls for being embedded in mortar of the wall, or for covering the face of the wall to either side of the joist, as the wall is built up around the end portion of the joist, the joist cap having an open bottom.

In the case where the end wall of the extension has a lip as described above, the lip preferably projects inwards from the end wall of the extension piece by an amount generally equal to the thickness of the end wall of the joist cap.

In accordance with a third aspect of the invention, there is provided a building having a joist capped by a joist cap assembly of the second aspect of the invention built into a wall of the building. Preferably, the flange portions of the joist cap and the flange-receiving channels of the extension piece are embedded in mortar within the thickness of the wall.

A specific embodiment of the present invention will now be described, purely by way of example, with reference to Figures 3A to 1OC of the accompanying drawings, in which: Figures lA-iF are a side view, front view, rear view, plan view, underplan view and isometric view from the front, above and one side of a known joist cap; Figure 2 is an isometric view of the joist cap fitted to an end portion of joist bearing on a partly-built wall; Figures 3A-3G are a side view, front view, rear view, plan view, underplan view, sectioned side view and isometric view from the front, above and one side of one embodiment of extension device according to the present invention; Figures 4A-B are a plan view and an isometric view of the extension device assembled with the joist cap; Figures 5A-B are isometric views of the assembly fitted to an end portion of joist bearing on a partly-built wall, with the assembly in its most contracted state fitted to a sawn timber joist in Figure 5A and approaching its maximum extension fitted to an engineered joist in Figure 5B; Figures 6A-B are isometric views of the parts of a two-part mould for forming the joist cap extension; Figures 7A-D are horizontally-sectioned views, taken on the section lines marked a-a to d-d in Figures 9A to 9C of the mould when open; Figures 8A-D are similar to Figures 7A-D, but with the mould closed; Figures 9A-C are vertically-sectioned views, taken on the section lines marked A-A to C-C in Figures 7A to 7D of the mould when open; and Figures bA-C are similar to Figures 9A-C, but with the mould closed.

Referring to Figures 3A to 3G, the extension piece 26 of the embodiment of the invention has: a main channel 28 with a rear wall 30 and a pair of side walls 32; and, at the front edges of the side walls 32, a pair of mutually facing flange-receiving channels 34 each having a rear waIl 36, a front waIl 38 and an interconnecting wall 40. In the relaxed state of the extension piece 26, the side walls 32 of the main channel 28 converge, as shown in Figures 3A- 3F, but in use the extension piece 26 is deformed so that the side walls 32 become generally parallel, as shown in Figure 3G.

Referring to Figures 4A and 4B, the extension piece 26 is fitted to a joist cap 10 as described above with reference to Figures 1A to IF, by sliding the end wall 12 and side walls 18 of the joist cap 10 into the main channel 28 of the extension piece 26 so that the side flanges 24 of the joist cap 10 engage in the flange-receiving channels 34 of the extension piece. The cross-sectional sizes of the joist cap 10 and extension piece 26, when their side walls 18,32 are parallel, are such that the joist cap 10 is a snug, telescopic, sliding fit in the extension piece 26.

The lower ends of the rear wall 30 and side walls 32 of the extension piece 26 are provided internally with lips 42,44 protruding from the rear and side walls 30,32 by an amount generally equal to the thickness of the end and side walls 12,18 of the cap 10, so that, when the cap 10 is fully inserted into the extension piece 26, the inwardly facing surfaces of the end and side walls 12,18 of the cap 10 merge smoothly with the inwardly facing surfaces of the lips 42,44. Also, cutaways 46 are formed at the lower ends of the flange-receiving channels 34 of the extension piece 26 so that restraint straps can be fitted between the wall and the joist without interfering with the joist cap 10 and extension piece 26. In an example, the height A of the lips 42,44 of the extension piece is 10 mm, the internal height B of the side walls 18 of the joist cap is 227 mm, and the overall height C of the extension piece 26 is 230 mm.

With these example measurements, the joist cap 10 may be used alone with a joist 14, as shown in Figure 2, and is a snug fit height- wise for a joist 14 having a height D of 225 mm.

The joist cap 10 and extension piece 26 may also be used in combination to provide a snug fit height-wise for joists 14 having a height D between, at one extreme, 235 mm as shown in Figure 5A and, at the other extreme, 400 mm as shown in Figure 5B whilst still providing a sufficient overlap � of at least about 57 mm between the joist cap 10 and the extension piece 26.

If a snug fit is required height-wise for joists 14 having a height of less than 225 mm, the joist cap 10 may be used alone with bottom portions of its end and side walls 12,18 trimmed off.

Alternatively, the space between the top of the joist 14 and the underside of the top wall 16 of the joist cap 10 can be filled with mortar or other filler material.

It should be noted that the joist cap 10 alone of a single size, or the combination of joist cap 10 and extension piece 26 of a single size, may be used with any thickness F of wall 20 greater than or equal to 100 mm, and that the flanges 22,24 of the cap 10 and the flange receiving channels 34 of the extension piece 26, if used, will be embedded in mortar within the thickness of the wall 20 so as to provide a good seal with the wall 20.

It will be seen, particularly in Figure 30, that the rear and front walls 36,38 of the flange-receiving channels 34 of the extension piece 26 are not continuous, but instead, for each channel 34, each wall 36,38 has a series of cutaways 48,50 offset from the cutaways 50,48 in the other wall 38,36. This enables the extension piece 26 to be injection-moulded using a two-part mould having a male mould part 52 and a female mould part 54 as will now be described with reference to Figures 6A to 1OC.

The mould parts 52,54 have respective joint faces 56,58 which are brought into abutment when the mould is closed. The male mould part 52 has a generally-cuboidal protrusion in front of its joint face 56, and the female mould part 54 has a generally-cuboidal recess 62 behind its joint face 58. The lower edges of the male protrusion 60 are rabbeted at 64. When the mould is closed, the protrusion 60 and recess 62 defme the mould space for the rear and side walls 30,32 of the extension piece 26, and the rabbets 64 provide the mould space for the lips 42,44. At each junction between a longer side of the protrusion 60 and the joint face 56 of the male mould part 52, a series of castellations 66 is provided. Also, at each junction between a longer side of the recess 62 and the joint face 58 of the female mould part 54, the mould part 54 is formed with a rabbet 67, and a further series of castellations 68 is provided in the rabbet 67 and spaced from the side wall of the rabbet 67. The castellations 68 of the female mould part 54 interdigitate with the castellations 66 of the male mould part 52 when the mould is closed. The castellations 64,66 are arranged so that, when the mould is closed, at some sections as shown in Figure 8A mould space 70 is provided for the interconnecting wall 40 and mould space 72 is provided for a portion of the rear wall 36 of the flange-receiving channel 34, but no mould space is provided for the front wall 38 of the flange-receiving channel 34; and at other sections as shown in Figure 8B mould space 70 is provided for the interconnecting wall 40 and mould space 74 is provided for a portion of the front wall 38 of the flange-receiving channel 34, but no mould space is provided for the rear wall 36 of the flange-receiving channel 34. Accordingly, when the mould is closed and molten plastics is injected into the mould through an injection port 76 (Figures 9A and 1OA) in the female mould part 54, material flows through the mould spaces and, in particular, to the series of mould spaces 72, thence to the continuous mould spaces 70, and thence to the series of mould spaces 74, and an extension piece 26 as shown in Figure 3G is formed. When the mould is opened and the extension piece 26 is ejected and cools, the extension piece relaxes to the shape shown in Figures 3A to 3E.

Although, in the embodiment of the invention described above, the flanges 22,24 of the joist cap 10 and the flange-receiving channels 34 of the extension piece 26 are intended to be embedded in mortar within the thickness of the wall, the joist cap and extension piece may be arranged so that the joist cap flanges and the flange-receiving channels overlap the face of the wall to either side of the joist. In this case, mastic or a foam rubber strip may be inserted between the face of the wall and the flanges and the flange-receiving channels to improve the seal.

It should be noted that the embodiment of the invention has been described above purely by way of example and that many modifications and developments may be made thereto within the scope of the present invention. -Il-

Claims

(The reference numerals in the claims are no: intended to limit the scope of the claims.) 1. An extension piece (26) for a joist cap (10) of the type having an end waIl (12) to cover the end face of a joist (14) that is to be built into a wall (20), a top wall (16) and a pair of side walls (18) extending from the end wall to cover the top and sides of an end portion of the joist and flange portions (22,24) projecting outwardly from the side walls for being embedded in mortar of the wall, or for covering the face of the wall to either side of the joist, as the wall is built up around the end portion of the joist, the extension piece comprising: a main channel portion (28) for receiving the joist cap and having an end wall (30) and a pair of side walls (32) for overlapping the end wall and side walls, respectively, of the joist cap; and a pair of mutually-facing flange-receiving channel portions (34) projecting outwardly from the side walls of the extension piece for receiving the flange portions of the joist cap; whereby the extension piece and the joist cap can be moved telescopically to vary the effective length of the extension piece and joist cap.
2. An extension piece as claimed in claim 1, wherein the end wall of the extension piece is formed, at one end of the extension piece, with an inwardly-projecting lip (42).
3. An extension piece as claimed in claim 2, wherein the side walls of the extension piece are also formed, at said one end of the extension piece, with inwardly-projecting lips (44).
4. An extension piece as claimed in any preceding claim wherein the flange-receiving channel portions stop short of one end of the extension piece.
5. An extension piece as claimed in claim 4 when dependent on claim 2 or 3, wherein said one end of the extension piece recited in claim 4 is the same as said one end of the extension piece recited in claim 2.
6. An extension piece as claimed in any preceding claim, wherein the main channel portion is open-ended at both ends thereof.
7. An extension piece as claimed in any preceding claim, wherein the extension piece is formed by injection moulding.
8. An extension piece as claimed in any preceding claim, wherein each flange-receiving channel has a pair of side walls (36,38) and a base (40), each side wall having a series of cutaways (48,50) offset from the cutaways in the other side wall of that flange-receiving channel.
9. An extension piece as claimed in any preceding claim, wherein, in the relaxed state of the extension piece, the side walls of the main channel portion converge towards each other in the direction away from the end wall.
10. An extension piece for a joist cap, substantially as described with reference to 3A to 1OC of the drawings.
11. A joist cap assembly, comprising: an extension piece as claimed in any preceding claim; and a joist cap having an end wall to cover the end face of a joist that is to be built into a wall, a top wall and a pair of side walls extending from the end wall to cover the top and sides of an end portion of the joist and flange portions projecting outwardly from the side walls for being embedded in mortar of the wall, or for covering the face of the wall to either side of the joist, as the wall is built up around the end portion of the joist, the joist cap having an open bottom.
12. A joist cap assembly as claimed in claim 11, when dependent directly or indirectly on claim 2, wherein the lip projects inwards from the end wall of the extension piece by an amount generally equal to the thickness of the end wall of the joist cap.
13. A joist cap assembly substantially as described with reference to 3A to bC of the drawings.
14. A building having a joist capped by a joist cap assembly as claimed in any of claims 11 to 13 built into a wall of the building.
15. A building as claimed in claim 14, wherein the flange portions of the joist cap and the flange-receiving channels of the extension piece are embedded in mortar within the thickness of the wall.